Oracle database creates the pga when oracle process starts

DBMS_PREPROCESSOR.PRINT_POST_PROCESSED_SOURCE
Retrieves the postprocessed source and then displays it with the function DBMS_OUTPUT.PUT_LINE

DBMS_PREPROCESSOR.GET_POST_PROCESSED_SOURCE
Returns the postprocessed source as either a single string or a collection of strings

SQL> BEGIN
2 DBMS_PREPROCESSOR.PRINT_POST_PROCESSED_SOURCE ( 3 'PROCEDURE', USER, 'POST_PROCESSED');
4 END;
5 /

PROCEDURE post_processed
IS
BEGIN
-- Fast and modern and easy
NULL;
END post_processed;

DBMS_PREPROCESSOR.GET_POST_PROCESSED_SOURCE (

'PROCEDURE', USER, 'POST_PROCESSED');

|| ' - '

|| rtrim ( l_postproc_code (l_row),chr(10))

Conditional compilation opens up all sorts of possibilities for PL/SQL developers and application administrators. And its usefulness only increases as new versions of the Oracle database are released and the DBMS_DB_VERSION constants can be put to full use, allowing us to take additional advantage of each version’s unique PL/SQL features.

PL/SQL and Database Instance Memory

The SGA is a group of shared memory structures, or SGA components, that contain data and control information for a single Oracle Database instance. All server and back‐ground processes share the SGA. Examples of data stored in the SGA include cached data blocks and shared SQL areas.

Process global area (PGA)